1 files changed, 75 insertions, 0 deletions
diff --git a/text/sentence.c b/text/sentence.c
new file mode 100644
index 0000000..4d3a7af
--- /dev/null
+++ b/text/sentence.c
@@ -0,0 +1,75 @@
+/* Sentence boundaries (UAX #29, Unicode 15.1): text/text.h. Extends and
+ * formats fold into the character before them (SB5); the rules after a
+ * sentence terminal look back through closing punctuation and spaces (kept
+ * as the pass goes) and, for SB8, ahead to the next letter (found for
+ * every position by one pass from the end). */
+#include "text.h"
+#include <stdlib.h>
+
+enum { OTHER = VEGA_SB_OTHER, CR = VEGA_SB_CR, LF = VEGA_SB_LF, EXTEND = VEGA_SB_EXTEND, SEP = VEGA_SB_SEP,
+       FORMAT = VEGA_SB_FORMAT, SP = VEGA_SB_SP, LOWER = VEGA_SB_LOWER, UPPER = VEGA_SB_UPPER, OLETTER = VEGA_SB_OLETTER,
+       NUMERIC = VEGA_SB_NUMERIC, ATERM = VEGA_SB_ATERM, SCONTINUE = VEGA_SB_SCONTINUE, STERM = VEGA_SB_STERM,
+       CLOSE = VEGA_SB_CLOSE };
+
+static bool paragraph_end(unsigned c) { return c == SEP || c == CR || c == LF; }
+static bool terminal(unsigned c) { return c == ATERM || c == STERM; }
+
+bool vega_sentences(const uint32_t *codes, size_t count, uint8_t *breaks) {
+    breaks[0] = count > 0; /* SB1 */
+    if (!count) return true;
+    uint8_t *eff = malloc(3 * count);
+    if (!eff) return false;
+    uint8_t *folded = eff + count, *stop = eff + 2 * count;
+    for (size_t i = 0; i < count; ++i) {
+        unsigned c = vega_sentence(codes[i]);
+        folded[i] = (c == EXTEND || c == FORMAT) && i && !paragraph_end(eff[i - 1]);
+        eff[i] = folded[i] ? eff[i - 1] : (uint8_t)c;
+    }
+    /* SB8's look ahead: from each position, the class of the first unit
+     * that is a letter, a paragraph end or a terminal (OTHER when none is). */
+    unsigned next = OTHER;
+    for (size_t i = count; i--;) {
+        unsigned c = eff[i];
+        if (!folded[i] && (c == OLETTER || c == UPPER || c == LOWER || paragraph_end(c) || terminal(c))) next = c;
+        stop[i] = (uint8_t)next;
+    }
+    /* After each unit: the terminal the text ends in, with only closes and
+     * then spaces after it (OTHER when it does not end so); whether spaces
+     * came yet; the unit before that terminal. */
+    unsigned term = OTHER, before_term = OTHER, previous = OTHER;
+    bool spaces = false;
+    for (size_t i = 0; i < count; ++i) {
+        if (folded[i]) {
+            breaks[i] = 0; /* SB5 */
+            continue;
+        }
+        unsigned B = eff[i];
+        if (i) {
+            unsigned A = previous;
+            bool join;
+            if (A == CR && B == LF) join = true;                                         /* SB3 */
+            else if (paragraph_end(A)) join = false;                                     /* SB4 */
+            else if (A == ATERM && B == NUMERIC) join = true;                            /* SB6 */
+            else if (A == ATERM && (before_term == UPPER || before_term == LOWER) && B == UPPER) join = true; /* SB7 */
+            else if (term == ATERM && stop[i] == LOWER) join = true;                     /* SB8 */
+            else if (term != OTHER && (B == SCONTINUE || terminal(B))) join = true;      /* SB8a */
+            else if (term != OTHER && !spaces && (B == CLOSE || B == SP || paragraph_end(B))) join = true; /* SB9 */
+            else if (term != OTHER && (B == SP || paragraph_end(B))) join = true;        /* SB10 */
+            else if (term != OTHER) join = false;                                        /* SB11 */
+            else join = true;                                                            /* SB998 */
+            breaks[i] = !join;
+        }
+        if (terminal(B)) {
+            before_term = previous;
+            term = B;
+            spaces = false;
+        } else if (term != OTHER && B == CLOSE && !spaces) {
+            /* still closing the sentence */
+        } else if (term != OTHER && B == SP) spaces = true;
+        else term = OTHER;
+        previous = B;
+    }
+    breaks[count] = 1; /* SB2 */
+    free(eff);
+    return true;
+}